Gated diode structure for eliminating RIE damage from cap removal

ABSTRACT

A semiconductor structure provided with a plurality of gated-diodes having a silicided anode (p-doped region) and cathode (n-doped region) and a high-K gate stack made of non-silicided gate material, the gated-diodes being adjacent to FETs, each of which having a silicided source, a silicided drain and a silicided HiK gate stack. The semiconductor structure eliminates a cap removal RIE in a gate first High-K metal gate flow from the region of the gated-diode. The lack of silicide and the presence of a nitride barrier on the gate of the diode are preferably made during the gate first process flow. The absence of the cap removal RIE is beneficial in that diffusions of the diode are not subjected to the cap removal RIE, which avoids damage and allows retaining its highly ideal junction characteristics.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices, and moreparticularly, to gated-diodes that includes capping dielectric layerswithin the active semiconductor structures.

BACKGROUND AND RELATED ART

Semiconductor diodes, in particular gated-diodes, are often used in CMOSintegrated circuits for important analog circuit functions includingtemperature sensing and bandgap reference voltage applications. For theanalog applications to properly function, the forward-bias diodecharacteristics should be nearly ideal, as measured by the diodeideality factor (n) which should be nearly equal to a value of 1. Inadvanced CMOS technologies, achieving a gated-diode structure with goodideality near 1 can be challenging because of the widespread use ofReactive Ion Etching (RIE), which can damage then semiconductorstructures. RIE related damage is known to degrade diode ideality. Thus,in order to achieve a good diode ideality, the RIE damage should beeliminated or minimized.

Diodes in general are formed by creating abutting semiconducting regionsof N-doped (excess electrons) and P-doped (excess holes). Preferably,one but not both regions is more heavily doped, creating either an N+/Pdiode or a P+/N diode. N-doped regions are typically formed byimplanting or diffusing N-type donor dopant species, such as arsenic orphosphorus, into the semiconductor material such as silicon. Similarly,P-doped regions are formed by implanting or diffusing P-type acceptordopant species, e.g., boron into a region adjacent to and contacting theN-type region. Typically, a dopant activation thermal cycle or heatingis necessary to make the dopants electrically active.

Gated-diodes formed as described, with the addition of a gate electrodeand gate dielectric located at or near the location of the P-N junction.Often but not always, the gate electrode serves as a masking structureto allow creating a self-aligned P-N diode wherein the edge of the gateelectrode defines the location of the P-N junction. Self-alignment canbe achieved when the P-N junction is formed by ion implantation, and thegate electrode is sufficiently thick to block either the heavier P+ orN+ region implant from penetrating through to the underlyingsemiconductor substrate, and is wide enough laterally to allow aphotolithography mask to consistently land on the gate even in thepresence of loose manufacturing alignment tolerances. Generally, it canbe advantageous to achieve good diode ideality by locating the P-Njunction underneath the gate electrode and gate dielectric because thisregion is typically a high quality interface largely free of defects.Avoiding defects in and around the P-N junction region is important forachieving good ideality, as defects are known to create generationand/or recombination sites which degrade the diode ideality.

Dielectric capping layers (such as nitride or oxide) on top of gates arecommonly used in CMOS fabrication. Examples of the uses for thesedielectric capping layers include use as a hard mask for gate electrodepatterning and increasing the gate stack thickness for ion implantationblocking effectiveness. A gate electrode hard mask is a layer or layerspatterned on top of a blanket gate electrode, which protects desiredregions from RIE, thus forming patterned gate electrodes. This is incontrast to soft mask based patterning where the pattern is formed usingphotoresist. Oftentimes it is beneficial to keep the dielectric hardmask on top of the gate even after the gate electrode etching has beencompleted and during subsequent ion implantation steps required forbuilding the gated-diode and Field Effect Transistors (FET). Theadditional dielectric layer contributes to blocking ion implantations,such as source/drain or halo implants from penetrating through the gateelectrode into the channel. The dielectric layer is typically removed byRIE prior to a silicide formation, to enable the gate electrode regionto be silicided. However, RIE can damage and introducing defects withinand nearby the gated diode (P-N junction) region, resulting in adegraded ideality, that ultimately leads to poor circuit functionalityin temperature sensor, bandgap reference voltage and other analogcircuits that rely on good diode ideality.

Generally, all the gates and diffusions of a sub 250 nm technology havesilicide formed to minimize resistance, knowing that silicidation ofsilicon and polysilicon regions reduces the resistance which results inincreased transistor and circuit performance.

FIG. 1 is a perspective view of a prior art structure for a diode and aFET as part of integrated circuit. For simplicity, a single N-FET isshown, but it should be understood that N-FETs and P-FETs can be usedtogether as part of CMOS integrated circuits. The fabrication sequencefor the conventional structure shown in FIG. 1 results in damage to thediode which degrades the diode ideality. Note that in this prior artstructure and P+/N diode is shown, but it should be understood that anN+/P diode can also be used.

Accordingly, there is a need for a structure that provides the benefitsof a dielectric capping layer on top of the gate electrode of thegated-diode to avoid the diode ideality degradation of removing thecapping layer that is desired for advanced CMOS integrated circuits.

SUMMARY

In one aspect, an embodiment of the invention provides a chip having anFET with a silicided high-K gate stack, source, and drain on highperformance devices, with an adjoining diode having a silicided cathodeand anode regions and a non-silicided high-K gate stack structure, theuse of silicide implying a gate first high-K metal gate process withpolysilicon in the stack.

In another aspect, an embodiment provides a polysilicon gate of thegated-diode that does not require silicidation as a gate terminal whichis not intended to carry a significant current if the gate dielectric issufficiently thick, such that the higher resistance of the non-silicidedpolysilicon is not a concern. The polysilicon gate of the gated-diodeseparates the cathode and anode implants, blocking the silicide betweenthe anode and cathode. Because the gate electrode of the gated-diodedoes not require siliciding, it avoids the need to remove the cap fromthe gate over the device. By protecting the gated-diode with resistduring a cap removal etching process, damage to the gated-diode due toetching can be avoided in view of etching a gate capping layer createsrecess and damage in silicon regions near the diode P-N junction thatdegrades the diode ideality. By avoiding damage, an excellent diodeideality can be achieved. With the cap layer in place on top of thegate, silicide is not formed on the gate, but as described previously,the gate terminal of a gated-diode does not need to carry significantcurrent. Hence, a higher resistance of non-silicided gate terminal isnot a concern.

In yet another aspect, a semiconductor structure is provided with asilicided high-K gate stack, source, and drain on high performanceNFETs/PFETs and a gated-diode having a silicided anode and cathoderegions and non-silicide HiK gate stack structure, the use of a silicideon the high-K gate stack of the FET implying a gate-first high-K metalgate process with polysilicon in the stack.

In still another aspect, a semiconductor integrated circuit is providedwith an n-FET and/or a p-FET having a silicided gate, source, drain, anda gated-diode with silicided anode and cathode regions, and anon-silicided gate. The NFETs/PFETs, gated-diodes and other active orpassive devices are connected to metal wiring to form an integratedcircuit.

In a further aspect, an embodiment provides a semiconductor structure ona substrate that includes an FET having a silicided source, a silicideddrain and a silicided gate stack; and a gated-diode adjacent to the FEThaving a silicided anode, a silicided cathode and a non-silicided gatestack, the non-silicided stack having a top surface covered by a layerof a material that inhibits silicide formation.

In still another aspect, an embodiment provides a method of forming asemiconductor structure that includes forming on a semiconductorsubstrate an FET having a silicided source, a silicided drain and asilicided gate stack; and forming a gated-diode adjacent to the FEThaving a silicided anode, a silicided cathode and a non-silicided gatestack, the non-silicided gate stack having a top surface covered by alayer of material that inhibits silicide formation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and whichconstitute part of the specification, illustrate the presently preferredembodiments of the invention which, together with the generaldescription given above and the detailed description of the preferredembodiments given below serve to explain the principles of embodimentsof the invention, wherein like reference numerals denote like elementsand parts, in which:

FIG. 1 shows a perspective view of a prior art diode and an FET as partof integrated circuit illustrating the damage to the diode degrading thediode ideality.

FIG. 2 illustrates a perspective view of the SOI substrate of FIG. 1following superimposing over a silicon substrate a buried oxide layer(BOX) followed by the SOI layer.

FIG. 3 depicts a perspective view of the structure illustrated in FIG. 2wherein a shallow trench isolation (STI) is formed in the SOI layerisolating the n-well from the p-well, followed by planarization such asCMP.

FIG. 4 shows ion implantation into different regions to form n-well andp-well regions.

FIG. 5 shows a perspective view of the formation of the gate stack thatincludes a gate dielectric, a gate electrode, and a hardmask.

FIG. 6 shows gate patterning using a photoresist.

FIG. 7 illustrates the resulting structure after etching the hardmask,transferring the photoresist pattern.

FIG. 8 is a perspective view of the structure after removing thephotoresist, leaving the etched hardmask in the desired pattern.

FIG. 9 shows the structure after etching the gate electrode and gatedielectric forming gates in the desired pattern.

FIG. 10 shows the structure after a conformal spacer material isdeposited.

FIG. 11 shows the resulting structure after etching the spacer material,preferably by a directional Reactive Ion Etch (RIE) process that removesthe spacer material from the horizontal surfaces while leaving it on thevertical sidewalls.

FIG. 12 illustrates opening areas by way of the photoresist masking toreceive N+ doping by ion implantation, the N+ region serving as sourcedrain regions of an NFET or the N-well contact of the diode.

FIG. 13 shows a photoresist masking step with open areas which are toreceive P+ doping by ion implantation, the P-dopant species preferablyincluding boron. The P+ region serves as the P+ portion of the diode orthe source drain region of the PFET (not shown).

FIG. 14 is a perspective view of the structure following the removal ofthe photoresist.

FIG. 15 shows a photoresist covering and protecting the diode whileexposing the FET region to an etch that removes the hardmask over thegate of the FET.

FIG. 16 illustrates the structure following RIE, highlighting resultingdamaged regions, wherein the photoresist covers the diode region,leaving the diode protected from the hardmask RIE, thus preserving thediode.

FIG. 17 shows the structure following the removal of the photoresist.

FIG. 18 depicts the structure after the formation of the silicide on theexposed N+ or P+ regions including the gate regions not covered by aspacer or by a hardmask, the diode gate remaining unsilicided while thehardmask is kept.

FIG. 19 shows a planar view of the structure shown in FIG. 18 includinga gated-diode and a FET, in this example an NFET.

FIG. 20 shows an embodiment with a gated-diode with a non-silicided gateformed with NFETs and PFETs provided with silicided gates.

FIG. 21 illustrates a planar view of the structure shown in FIG. 20,including a gated-diode and a NFET and a PFET.

FIG. 22 shows a plan view of an embodiment of an alternate diodestructure illustrating additional plan-view designs of gated-diode, inan embodiment showing the gated-diode formed within the perimeter of thegate.

DETAILED DESCRIPTION

Detailed embodiments of the methods and structures of the presentdisclosure are described herein; however, it is to be understood thatthe disclosed embodiments are merely illustrative of the describedmethods and structures that can be embodied in various forms. Inaddition, each of the examples given in connection with the variousembodiments of the disclosure is intended to be illustrative, and notrestrictive. Further, the figures are not necessarily to scale, somefeatures can be exaggerated to show details of particular components.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as a representativebasis for teaching one skilled in the art to variously employ themethods and structures of the present disclosure. For purposes of thedescription hereinafter, the terms “upper”, “lower”, “top”, “bottom”,and derivatives thereof shall relate to the disclosed structures, asthey are oriented in the drawings.

Referring to FIG. 2, an illustrative structure and a method for formingsemiconductor FET devices on a semiconductor-on-insulator (SOI)substrate are described.

FIG. 2 shows a substrate [100], presently Silicon-on-Insulator (SOI).The SOI layer [102] is located above the buried-oxide layer (BOX) [101]and the substrate [100]. The buried oxide (BOX) layer [101] on thesubstrate [100] can be made as a silicon oxide, a nitride, a siliconnitride, and/or an oxynitride, e.g., silicon oxynitride, having athickness ranging from 5 nm to 1000 nm, or preferably, from 10 nm to 200nm, and still more preferably, from 10 nm to 25 nm.

The semiconductor-on-insulator (SOI) substrate can be employed as thesemiconductor substrate. When employed, the SOI substrate includes ahandle substrate superimposed by a buried insulator layer located on anupper surface of the handle substrate, and a semiconductor device layerlocated on an upper surface of the buried insulator layer. The handlesubstrate and the semiconductor device layer of the SOI substrate caninclude the same or different semiconductor material. The term“semiconductor” as used herein in connection with the semiconductormaterial of the handle substrate and the semiconductor device layerdenotes any semiconducting material including, for example, Si, Ge,SiGe, SiC, SiGeC, InAs, GaAs, InP or other like III/V compoundsemiconductors. Multilayers of these semiconductor materials can also beused as the semiconductor material of the handle substrate and asemiconductor device layer [102]. In one embodiment, the handlesubstrate [100] and the semiconductor device layer are both made of Si.

The handle substrate and the semiconductor device layer can have thesame or different crystal orientation. For example, the crystalorientation of the handle substrate and/or the semiconductor devicelayer can be {100}, {110}, or {111}. Other crystallographic orientationsbesides those specifically mentioned can also be used in the presentdisclosure. The handle substrate of the SOI substrate can be a singlecrystalline semiconductor material, a polycrystalline material, or anamorphous material. The semiconductor device layer of the SOI substrateis a single crystalline semiconductor material. A single crystallinesemiconductor material (or monocrystalline semiconductor material) is asemiconductor material in which the crystal lattice of the entire sampleis continuous and unbroken to the edges of the sample, with no grainboundaries.

The buried insulator layer of the SOI substrate can be a crystalline ornon-crystalline oxide or nitride. In one embodiment, the buriedinsulator layer is made of oxide. The buried insulator layer 101 can becontinuous or it can be discontinuous. When a discontinuous buriedinsulator region is present, the buried insulator region exists as anisolated island that is surrounded by semiconductor material.

The SOI substrate can be formed utilizing standard processes includingfor example, SIMOX (separation by ion implantation of oxygen) or layertransfer. When a layer transfer process is employed, an optionalthinning step can follow the bonding of two semiconductor waferstogether. The optional thinning step reduces the thickness of thesemiconductor layer to a layer having a thickness that is moredesirable.

The thickness of the semiconductor device layer of the SOI substrate istypically from 100 Å to 1000 Å, with a thickness from 500 Å to 700 Åbeing more typical. In some embodiments, and when an ETSOI (extremelythin semiconductor-on-insulator) substrate is employed, thesemiconductor device layer of the SOI has a thickness of less than 100Å. If the thickness of the semiconductor device layer is not within oneof the above mentioned ranges, a thinning step such as, for example,planarization or etching can be used to reduce the thickness of thesemiconductor device layer to a value within one of the ranges mentionedabove.

Referring to FIG. 3, a shallow trench isolation (STI) [103] created by afabrication sequence is shown including trench etching, dielectricdeposition such as oxide, followed by planarization such as CMP. Theisolation formed by the STI process includes patterning (e.g.,deposition a sacrificial pad layer (e.g., pad oxide and pad nitride),patterning (e.g., by lithography) and etching STI trenches, preferablyby reactive ion etch (RIE), filling the trenches with one or multipleinsulators including but not limited to oxide, nitride, oxynitride,high-k dielectric, or any suitable combination of those materials. Theplanarization process, such as chemical-mechanical polishing (CMP), canbe used to provide a planar structure. Besides STI [103] other isolationsuch as mesa isolation, local oxidation of silicon (LOCOS) can also beused. The sacrificial pad oxide and pad nitride can then be stripped.

FIG. 4 shows ion implantation into different regions to form n-well[104] and p-well [105] regions. The n-well ion implantation can ben-type dopant elements including arsenic or phosphorus. The p-well ionimplantation preferably uses a p-type dopant material, including boronor indium.

Referring to FIG. 5, forming a gate stack is illustrated including agate dielectric [106], a gate electrode [107], and a hardmask [108]. Thegate dielectric [106] can be selected from silicon oxide, siliconoxynitride, nitride, high-K materials such as hafnium oxide or stackedcombinations thereof. Gate electrode [107] is a conductor orsemiconductor, e.g., polysilicon or metal, e.g., TiN, or stackedcombinations thereof. The polysilicon layer can be doped by way of ionimplantation or in-situ doped during the deposition. The hardmask [108]is typically a dielectric, e.g., silicon oxide, silicon nitride or astacked combination thereof.

Referring to FIG. 6, gate patterning is shown preferably usingphotoresist, a mask exposure using optical source, and photoresistdevelopment leaving the photoresist in desired areas [109].

FIG. 7 shows the resulting structure after etching the hardmask,preferably using a RIE process, and transferring the photoresist patterninto the hardmask.

Referring to FIG. 8, the structure is shown following the removal of thephotoresist by way of a stripping process, leaving the etched hardmaskin the desired pattern.

FIG. 9 shows the structure after etching the gate electrode [107] andgate dielectric [106], preferably using a directional RIE, forming gatesin the desired pattern.

FIG. 10 shows the structure following the deposition of a conformalspacer layer [110]. The spacer material is preferably a dielectric suchas silicon nitride or silicon oxide that can be deposited by way ofChemical Vapor Deposition (CVD), Atomic Layer Deposition (ALD) orMolecular Layer Deposition (MLD).

FIG. 11 illustrates the resulting structure after etching the spacermaterial, preferably using a directional Reactive Ion Etch (RIE) totremove the spacer material from the horizontal surfaces but keeping iton the vertical sidewalls.

FIG. 12 shows a photoresist masking [111] that opens areas that are toreceive N+ doping by ion implantation [112]. N-dopant materialspreferably include arsenic or phosphorus. The N+ region serves as thesource drain region of an NFET or as the N-well contact of the diode.Alternatively, the N+ region could be formed by etching a trench andfilling it with epitaxially deposited semiconductor, such as N-dopedSiC.

FIG. 13 shows a photoresist masking step [113] that opens areas set toreceive P+ doping by ion implantation [114]. P-dopant materials mayinclude boron. The P+ region serves as the P+ portion of the diode orthe source drain region of the PFET (not shown). The photoresist is thenremoved, resulting in the structure shown in FIG. 14. Alternatively, theP+ region can be formed by etching a trench and filling it withepitaxially deposited semiconductor, such as P-doped SiGe.

FIG. 15 illustrates the photoresist step which covers and protects thediode, while exposing the FET region to etching that removes thehardmask [108] over the FET gate. The hardmask etch is preferablyperformed by RIE etching. The RIE etching can result in damaging theexposed regions as will be illustrated with reference to FIG. 16.

Referring to FIG. 16, the structure is shown following RIE etching,illustrating the resulting damaged regions [116]. Because thephotoresist [115] covers the diode region, it protects the diode fromhardmask RIE damage, and preserves not only the diode, but it alsoavoids degradation of the diode ideality.

FIG. 17 shows the structure following the removal of the photoresist.

FIG. 18 shows a cross-section view of the structure after silicide [117]formation. The silicide can be selected from nickel silicide, titaniumsilicide, cobalt silicide, or any other silicide material. The nickel,titanium, cobalt or other similar metal is deposited on the entirestructure. During at heating of the wafer, preferably by Rapid ThermalAnnealing (RTA), the silicide forms as a reaction between the metal andthe silicon on the exposed N+ or P+ regions including gate regions notcovered by spacer [110] or the hardmask [108]. The FET gate is silicidedleaving the diode gate unsilicided as a result of the hardmask stillremaining in place. The unreacted metal on the spacer or the hardmask isetched away, preferably by aqueous chemistry.

Still referring to FIG. 18, in one embodiment, the gated-diode shown isdevoid of any damage resulting from the absence of siliciding the gate,and is further formed alongside the FET having a silicided gate thatallows it to achieve a high-performance caused by the reduced gateresistance.

FIG. 19 shows an embodiment wherein the gated-diode with itsnon-silicided gate is formed alongside the NFET and PFET having asilicided gate. It should be noted that while the gated-diode is shownas a P+/N diode, an embodiment of the inventive structure could beequally applicable to a N+/P diode.

FIG. 20 shows a plan view of the structure illustrated in FIG. 18depicting additional details of the structure. The non-silicided gate[123] of the gated-diode is shown in the region on top of the activeregion of the device, leaving the cap layer in place within the activeregion, thereby avoiding RIE damage to the active region of the diode.The gate [121] of the gated-diode is silicided outside the active regionto the diode, over the STI, by removing the cap layer in the statedregion that allows silicide to form. The silicide within the regionenables a good contact between the contact [120] and the gate [121] ofthe gated-diode. Removing the cap layer in the region outside of theactive area of the gated-diode does not create damage near the activeregion of the diode. Shown in FIG. 20, the gate of the FET is silicided[122].

FIG. 21 shows a plan view of the structure from FIG. 19, illustrating anembodiment of the gated-diode with a non-silicided gate [124] and NFET[125] and PFET [126] with a silicided gate. The gate of the gated-diodeis not silicided [124] in the region above the active region of thedevice, and leaving the cap layer in place within this region, making itpossible to avoid RIE damage in the active region of the diode. The gateof the gated-diode is silicided outside the diode active region [122],over the STI, by removing the cap layer in this region, thus enablingsilicide to be formed. The silicide in this region provides good contactbetween the contact [120] and the gate of the gated-diode. Removing thecap layer in the region outside of the active area of the gated-diodedoes not create damage near the active region of the diode. The gate ofthe FETs [125, 126] is silicided.

FIG. 22 shows a plan view of an embodiment of an alternate diodestructure illustrating other plan-view designs of the gated-diode (NFETand PFET not shown). In an embodiment, the diode is formed within theperimeter of the gate. As previously described, the gate of thegated-diode is not silicided [128] in the region located above theactive region of the device by leaving the cap layer in place in thisregion, to avoid RIE damage within the active region of the diode. Thegate of the gated-diode is silicided [127] in an area beyond the diodeactive region and spanning over the STI, and removing the cap layer fromthe region, thereby permitting the formation of silicide.

While the present disclosure has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details can be made without departing from the spirit and scope ofthe present disclosure. In one therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A semiconductor structure on a substratecomprising: an FET having a silicided source, a silicided drain and asilicided gate stack, said silicided gate stack comprising a gatedielectric layer on top of said substrate, a semiconductor gateelectrode on top of said gate dielectric, and a silicided layer on topof said semiconductor gate electrode; and a gated-diode adjacent to saidFET having a silicide anode, a silicide cathode and a non-silicided gatestack, said non-silicided gate stack comprising a gate dielectric layeron top of said substrate, a gate electrode substantially made ofsemiconductor on top of said gate dielectric, said gate electrode havinga top surface covered by a layer of material that inhibits saidnon-silicided gate stack to be silicided.
 2. The structure as recited inclaim 1 wherein a region surrounding the gated-diode is isolated fromdamage caused by RIE etching.
 3. The structure as recited in claim 1,wherein said substrate is an SOI substrate, a bulk or a single crystalsemiconductor.
 4. The structure as recited in claim 3, comprising ann-well and a p-well above said substrate.
 5. The structure as recited inclaim 4, wherein said n-well and p-well are isolated by an STI.
 6. Thestructure as recited in claim 4, wherein said gated-diode in one of then-well or p-well, and said FET are respectively on said n-well or saidp-well.
 7. The structure as recited in claim 6 wherein said gate-diodestack comprises a gate dielectric, a gate electrode, and a hardmask. 8.The structure as recited in claim 6, wherein said gated-diode stack isterminated by a dielectric layer that inhibits silicide formation. 9.The structure as recited in claim 1, wherein said gate stack comprises agate electrode made of semiconductor.
 10. The structure as recited inclaim 1 wherein said gate stack comprises a gate dielectric made of ahigh-K dielectric.